Treatment of zinciferous materials containing cadmium



I Patented Aug. 4, 1931 UNITED STATES PATENT OFFICE HOWARD M. CYR AND ROBERT K. WARING, F PALMERTON, PENNSYLVANIA, ASSIGN- ORS TO THE NEW JERSEY ZINC COMPANY, OF NEW YORK, N. Y., A CORPORATION OF NEW JERSEY TREATMENT OF ZINCIFEROUS MATERIALS CONTAINING CADMIUM No Drawing.

This invention relates to the treatment of zinciferous materials containing cadmium and perhaps other contaminating metals. The invention aims to provide an improved method of effecting a substantial removal or elimination of cadmium from such zinciferous materials without any appreciable loss of zinc. More particularly, the invention contemplates an improved pyrometallurgical treatment for so reducing the cadmium content of zinciferous materials, without substantial loss of zinc, that high grade zinc products can be produced therefrom by customary methods of smelting. While of more especial technical advantage in removing cadmium, the invention contemplates the removal from zinciferous material of other contaminating metals, particularly lead.

Cadmium and zinc are very similar metal- 'lic' elements in both chemical and physical properties. Indeed, in the zinc industry and in text books on metallurgy, it is common to think and treat of these two metals as very closely related. In all pyrometallurgical processes of zinc extraction, the cadmium follows the zinc, so that no complete separation of the two metals is possible. Accordingly, the presence of a relatively small percentage of cadmium in a zinc ore, or other .zinciferous material, prevents the pyrometallurgical production therefrom of high grade zinc products, such as zinc metal, zinc oxide, zinc dust, etc., substantially free of ,cadmium. Cadmium and lead are technically the most commonly recognized contaminants of zinc ores and their concentrates.

In addition, certain metals, such as tin, antimony, bismuth, etc. are commonly present in zinc ores. i Appreciable amounts of these contaminating metals, more especially cadmium and lead, find their way into the product of the zinc recovery operation and thereby contaminate the zinc product vob- I tained therefrom.

Application filed October 15, 1929. Serial No. 399,875.

roasting in'the presence of a chloridizing agent and water vapor. While sodium chloride would appear to be the most available and economical chloridizing agent in the practice of that method, we have. discovered, in the course of 'a thorough and careful practical investigation of the method,

usually necessary, when employing sodium chloride as the chloridizing agent, to subject the zinciferous material to two or even more consecutive chloridizing sintering treatments before the cadmium content is sufliciently reduced to permit the production of high grade zinc products by the heretofore customary pyrometallurgical processes of zinc recovery.

Our present invention, based on the foregoing discovery involves subjecting the zinciferous material to a heat treatment operation in the presence of a chloridizing agent and water vapor under conditions of basicity favorable to effective utilization of acidic compounds of chlorine for chloridizing cadmium and/or other contaminating metals. Such conditions of basicity are preferably brought about by avoiding the formation of strongly basic reaction products, such as sodium oxide. This may be advantageously effected by adding zinc chloride, preferably in the form of an aqueous solution thereof, to the zinciferous material, or by chloridizing a small portion of the zinc in the zinciferous material, either before the heat treatment or while it is in progress, by reagents that do not form Where a strongly basic reaction product is formed, the conditions of basicity characteristic of the invention may be brought about by associating with the zinciferous material (by reaction or otherwise) a suitable acidic substance or reaction product capable of neustrongly basic reaction products.

and thereby permitting effective utilization of the chloridizing agent.

The invention can be carried out in practice in a number of different ways. Merely by Way of illustration, We will first describe What is now our preferred practice in treat- ,ing a zinc flotation concentration containing about 65% Zinc, from 35% lead and about 0.12% cadmium, in accordance with the principle of the invention. The concentrate is first subjected to an ordinary desulfurizing or roasting treatment carried out in any appropriate roasting apparatus. The roasting need not be carried to completion as any residual sulfide sulfur serves asfuel in the subsequent sintering operation and thus replaces an equivalent amount of coal. The roasted concentrate is then mixed with an appropriate amount of coal and a solution of zinc chloride containing the proper amount of water and of zinc chloride. If the concentrate is completely roasted, 5% by weight of anthracite dust coal or coke fines has been found .to give satisfactory'results. The amount of Water used must be that which gives the resulting mixture the proper consistency. Proper consistency may be defined as that consistency which gives a maximum porosity ful since it causes an objectionable loss of zinc. In the exampleunder discussion, 5% by Weight of zinc chloride gives satisfactory results.

The mixing and heat treatment operations of the invention may be advantageously carried out in a Dwight-Lloyd sintering apparatus with the mixing, crushing and screening equipment commonly employed therewith. The mixing should be so conducted as to yield a fiufly product rather than a dense, compact one. The sintering operation shouldbe conducted to produce uniform, porous sinter in order to obtain the maxi ium removal of cadmium and lead. The suction in the windbox of the sintering machine is regulated to draw a sufiicient amount of air through the charge so that the sinterei product discharged at the end of (vine is not red hot and fuming. The atilizcd fume may be collected by any appropriate method and its cadmium, lead and zinc con-tent recovered. The lead and cadmium may be recovered by taking the fume into aqueous solution and replacing lead and cadmium by zinc. If desired, the resulting zinc chloride solution may be returned for use in the sintering operation, supplemented by the addition of such small amount of fresh zinc chloride, or other appropriate source of chlorine including even sodium chloride, as may be necessary to compensate for losses in chlorine.

A very substantial elimination of cadmium and lead is effected by a single chloridizing sintering operation carried out in the manner just described. Thus, for example, starting with a roasted flotation concentrate containing about zinc, from 35% lead and about 0.12% cadmium, a single chloridizing sintering treatment carried out as described produced a sintered product of substantially the same zinc content and containing less than 0.0025% cadmium and less than 0.1% lead. Under the heretofore customary procedure using sodium chloride as the chloridizing agent, as described in the aforementioned Teter application, at least two consecutive chloridizing sintering operations are necessary to effect the reduction in the cadmium and lead content of this same roasted concentrate which is effected in a single chloridizing sintering operation conducted in accordance with our invention.

The improved results attained by the practice of the invention are due to the action, as

the chloridizing agent, of zinc chloride in the absence of strongly basic products. It is our belief that during the sintering operation the zinc chloride, zinc oxide and Water, present in the mixture undergoing treatment, react to form zinc oxychloride. Thezinc oxychloride is not stable at the temperature attained during sintering and probably dissociates into zinc oxide and hydrochloric acid. The ultimate reaction, omitting intermediate steps, may be expressed by the following equation The hydrochloric acid formed in this ner chloridizes cadmium and lead as Well as more zinc. The cadmium chloride and lead chloride are volatilized and driven out of the charge while the zinc chloride is again converted to Zinc oxide and hydrochloric acid as represented by the foregoing equation, Thus, by the practice of the. invention, cadmium and lead are volatilized as chlorides without volatilizing any appreciable amount of zinc chloride, in spite of the fact that zinc chloride has a higher vapor pressure either cadmium chloride or lead chloride.

The superior of Zinc chloride chloridizing ag and/or lead fro tributable we believe to (1} its strong cal attraction for water, {72) 1 is an excellent flux, and t the factthat i n a a b is readily hydrolyzed and forms an oxide which is not strongly basic. 1

The strong chemical attraction of zinc chloride for Water increases the amount of water required to attain the proper conslstency of the zinciferous charge prepared for sintering. It is also significant that the use of zinc chloride not only requires the use of additional water to attain proper-consistency, but that this Water is not driven off, during sintering, until a higher temperature is reached. This additional water in the charge prepared for sintering has three advantages, namely:

I a The drying out of the bed, especially the lower part, is retarded; thus maintaining the proper consistency for a longer time. This explains the fact thatin practice the use of zinc chloride makes it possible-to obtain a more uniform sinter.

(b) The formation of more hydrochloric acid by the hydrolysis of zinc chloride is made possible, the reaction being represented by the equation hereinbefore given.

(a) The increase inthe hydrolysis of zinc chloride caused by the additional water will also decrease the loss of zinc by volatilization.

The fact that zinc chloride is an excellent flux promotes, we believe, the-release of cadmium from certain ores in which it is intimatelyinterlocked' with the zinc.

In the hydrolysis of zinc chloride, represented by the foregoing equation, there results an oxide (ZnO) which is not strongly basic and hydrochloric acid, a powerful chloridizing agent. Due to the absence of any strongly basic reaction product, the hydrochloric acid, resulting from the hydrolysis of zinc chloride, is available in large part, if not wholly, for the chloridizing of cadmium and lead. On the other hand, when using sodium chloride as the chloridizing agent, hydrochloric acid, when formed as an intermediary reaction product, is at least partially neutralized by sodium oxide (also an intermediary reaction product) which is a strong base.

The action of sodium chloride, as the chloridizing agent, may be summarized by the following equations:

( 1) QNaCl ZnO ZnCl Na O (2) ZnCl H .O ZnO QHCl (3) Na O 2HCl H O QNaCl Consideration of the foregoing equations shows that, in addition tothe detrimental effect of the strongly basic intermediary reaction product formed, there isanother very important factor to be considered, namely the speed of reaction. Using zinc-chloride as a chloridizing agent, in accordance with our invention, only one reaction (zinc chloride plus water) is necessary to form hydrochloric acid-the active chloridizing agent. However, when sodium chloride is used as a chloridizing agent, the preliminary, and relative- One reason for this is undoubtedly the fact that inthe former case the time for reaction istwice as long as in the latter. The same beneficial effect of increasing the time for reaction is obtained in the practice of the present invention by increasing the speed of reaction in consequence of the elimination of the preliminary reaction (foregoing equation 1) resulting from the use of zinc chloride as the chloridizing agent.

It is undoubtedly true that in any chloridizing sintering of zinciferous material the chloridizing agent at first forms chlorides of the available metals, including zinc, cadmium and lead. The relative amount of zinc chloride is large due to the preponderance of zinc over the other metals in the'zinciferous material, and the chloridization of the other metals by this first reaction is incomplete. As prediously intimated, it is our belief that the remaining cadmium and lead are chloridized at the expense of the zinc chloride. Where, therefore, as in our present invention, the presence of zinc chlorideand the absence of strongly basic products are as- 100 sured, substantially complete elimination of the usual percentages of the contaminating metals is effected ina single chloridizing sintering operation.

The importance of water in the reactions necessary for eflicient chloridization has already been pointed out. From a physical standpoint water is necessary to obtain the desired uniform porosity of the bed. During the sintering operation there is an inevitable tendency for the bottom of the bed to dry out before the operation has reached completion. This usually results in poorer sinter in the bottom part of the bed than in the top.

It is evident that this effect would be decreased by increasing the amount of water. in

the charge.

From a chemical standpoint water is essential, because it reacts with zinc chloride to form hydrochloric acid and zinc oxide thus serving the double purpose of facilitating the chloridization of lead and cadmium, by the production of hydrochloric acid, and reducing the zinc loss by converting volatile zinc chloride into non-volatile zinc oxide.

From the law of mass action it is evident that these desirable effects would be increased by increasing the amount of water in the charge.-

The use of zinc chloride, as the chloridizing agent, permits the use of relatively more water in the charge prepared for sintering, as hereinbefore explained. We have further found that relatively more water can be added to the charge, without rendering the harge too doughy or pulpy for the production of sufficient porosity during the subsequent sintering, if the mechanical work done to effect mixing be restricted to that absolutely necessary to secure a proper blending of the zinciferous material, fuel, water and reagents. In practice, the amount of work done in mixing the charge may be decreased by decreasing the time of mixing and/or by modifying the heretofore customary method of mixing the charge for sintering. Thus, decreasing the mixing time in a Werner- Pfieiderer laboratory batch mixer from 3 minutes to 1 minute permits a substantial increase in the water content of the charge. Also, by modifying a Dwight-Lloyd mixer so as to shorten the path of the mixture and by using a relatively shallow bed, the permissible water-content of the charge may be increased enormously over that possible when the mixing is done in a pug mill or in the usual Dwight-Lloyd mixer. The use of the. shallow bed permits a certain amount of rolling of the mixture which causes lumps to form. It has been. found possible to prev ventlump formation by increasing the speed of the paddles. The formation of rings of wet ore in the spaces between the paddles can be overcome either by widening the paddles or by increasing the number of paddles. The effectiveness of varying the water content of the charge by varying the work done in mixing is different for different ores. In

- general, it is greatest with a very fine particle size ore such as a flotation concentrate and becomes substantially negligible with coarse gravity or magnetic concentrates.

The proper amount of water to be incorporated in the charge prepared for sintering will depend on the chemical composition of the ore or other zinciferous material, on the particle size of the ore, on the mixing procedure, and on the chloridizing agent used. reating a roasted flot tion concentrate. such as hereinbefore descrited, the charge prepared for sintering may contain 30% by weight of water, whereas in the treatment of a relatively coarse gravity or magnetic concentrate the permissible amount of water incorporated in the charge may be as little as 5% by weight. It has been found harmful to wet the zinciferous material at time prior the preparation of the In? d charge for sintering. This has been found to be the cas even where the material is again drie before the mixing operatic Another factor which T have found to ma terially influence the e iency cadmium and lead elimination is the of time of ignition in the sintering operation. in the past, it has, of course, been realived that the ignition time must be sufficient to thoroughly ignite the top of the bed, but any extension of the time beyond this period was considered unnecessary. \Ve have found it advantageous to prolong the ignition of the sin'tering charge beyond the time necessary to ignite the surface layer, the optimum time of ignition de pending on the ignition apparatus employed. WVe have obtained a marked improvement in the elimination of cadmium and lead by extending the ignition period to a duration six times that required to ignite the top of the charge.

The elimination of the cadmium and lead, in accordance with the invention, may be accomplished by the use of chloridizing agents other than zinc chloride, but in any case zinc chloride should be formed either prior to or during the heat treatment operation. Thus, the zinc chloride maybe formed by chloridizing part of the zinc in the material to be treated. This can be conveniently accomplished, especially with oxidized or roasted ores, by adding dilute hydrochloric acid to the ziuciferous material in place of the aqueous solution of zinc chloride hereinbefore described. Hydrochloric acid gay be formed in the zinciferous material by adding thereto sulfuric acid and sodium chloride, in which case the sulfuric acid reacts in part with the sodium chloride to form sodium sulfate and hydrochloric acid. Sodium oxide may, it is true, be subsequently formed by the thermal de-' composition of the sodiumsulfate during the ensuing sintering operation, but this decomposition liberates sulfur trioxide and/or sulfur dioxide at the same time, the acidity of which tends to reduce the basicity due to the formation of the sodium oxide, and to neutralize its deleterious effects. Furthermore, the sulfuric acid likewise forms zinc sulfate with the zinc oxide present in the zinciferous material. This zinc sulfate is decomposed during the subsequent sintering to zinc oxide, a base of moderate strength, and sulfur trioxide and/or sulfur dioxide, strong acids. These reactions set up conditions that inhibit the strongly basic intermediary reaction product (sodium oxide) from diminishing the effectiveness of the chloridizing agent. It is evident from these last discussed reactions that zinc sulfate may be used (as a substitute for sulfuric acid) with sodium chloride or other alkaline or alkaline earth chloride to provide the active chloridizing agent under conditions incapable of rendering the chlorine present unavailable for its contemplated useful chloridizing action.

It is to be understood that sodium chloride is mentioned in the preceding paragraph merely by way of example and that this phase of the invention is not restricted thereto. Gther alkaline or alkaline earth chlorides can be used, such as calcium chloride, barium chloride, and the like. It is further to be understood that use may be made of acids other than sulfuric acid which give substantially the same end results in the sintering operation.

While we have particularly specified a sintering operation by blast-roasting as our pre- 1 ferred type of heat treatment operation, it is to be understood that the invention is not restricted to that particular type of heat treatment. In its broad aspect, the invention may be carried out by any heat treatment operation adapted to effect the contemplated chloridizing action. It is characteristic of the invention that the heat treatment, in conthe United States by junction with the chloridizing agent and Water vapor under conditions of basicity incapable of rendering the chlorine compounds present unavailable for the contemplated useful chloridizing action, effects the removal of the contaminating metals by volatilization. The gaseous products of the heat treatment operation should be removed under conditions substantially inhibiting condensation of any metal chlorides within the charge undergoing treatment. Such removal of the gaseous products of the operation may be advantageously accomplished by maintaining an appropriate gaseous current through the charge of zinciferous material while subjected to the heat treatment.

The purity of commercial zinc products is graded according to their cadmium, lead and iron content. The following specifications have been adopted for zinc metal (spelter) in the American Society for Testing Materials.

' High Inter- Brass Prime grade mediate special selected western Cadmium, not more than 0. 07% 0. 0. 50% 0. 75% lNo imit Lead, not more than... 0.07 0.20 0. 0. 80 1. 60% Iron, not more than 0. 03 0.03 0.03 O. 04 0.08

While the grades shown above are the oflirial specifications, the commercial distinctions are high grade virgin, redistilled, brass special, and prime western. High grade-virgin metal comprises that made from Franklin, N. J ores by pyrometallurgical methods, and that made from certain other zins ores by electrolytic processes.

Applying our present invention to the treatment of zinc ores from which heretofore only the lower grades of zinc metal could be produced by customary pyrometallurgical methods, we have been able to eliminate the cadmium and lead to such an extent that zinc metal equal in purity to high grade virgin metal may be produced therefrom in a furnace of the ordinary multiple retort type. Furthermore, zinc metal containing 99.99 zinc may be produced from such ores treated in accordance with the invention and subsequently smelted or reduced in the form of colred agglomerates in a vertical retortfurnace with lead elimination, in accordance with the practice described in United States Patent No. 1,712,132.

We claim 1. The improvement in the treatment of zincifcrous material containing cadmium which comprises subjecting the material to a heat treatment operation in the presence of a chloridizing agent and water Vapor and under conditions of basicity favorable to efstrongly basic reaction products and thereby effecting the removal from the material by volatilization of such an amount of'cadmium without substantial loss of zinc that the sotreated material is of sufiiciently low cadmium content for the pyrometallurgical production of a high grade zinc, product therefrom.

3. The improvement in the treatment of zinciferous material containing cadmium which comprises subjecting the material to a sinterin g operation by blast-roasting in the presence of a chloridizing agent and water.

vapor and under conditions of basicity favorable to efi'ective utilization of acidic compounds of chlorine for chloridizing cadmium and thereby effecting the removal from the material by volatilization of such an amount of cadmium without substantial loss of zinc that the cadmium'content of the so-treated material is sufficiently low for the production of high grade zinc products therefrom by customary pyrometallurgical methods. I

4. The improvement in the treatment of zinciferous material containing cadmium which comprises subjecting the material to a sintering operation by blast-roasting in the presence of a chloridizing agent and water vapor and under conditions incapable of forming strongly basic reaction products and thereby effecting the removal from the material by volatilization of such an amount of cadmium without substantial loss of zinc that the cadmium content, of the so-treated material is sufliciently low for the production of high grade zinc products therefrom by customary pyrometallurgical methods.

5. The improvement in the treatment of zinciferous material containing cadmium which comprises subjecting the material to I ing mixture to a sintering operation by blastroasting in the course oi which a large proportion of the initial cadmium content of the zinciterous material is removed by volatilization without substantial loss of zinc.

7. The improvement in the treatment of zinciferous material containing cadmium which comprises mixing the material with an aqueous solution of hydrochloric acid, and heating the resulting mixture in the presence of water Vapor and thereby effecting the removal from the material by volatilization of an economically significant amount of cadmium without substantial loss of zinc.

8. The improvement in the treatment of zinciferous material containing cadmium which comprises mixing the material with an aqueous solution of a. chloridizing agent until there is uniformly distributed throughout the material a suflicient amount of zinc chloride to chloridize all the cadmium therein, subjecting the resulting mixture to a heat treatment operation in the presence of water vapor, and maintaining a gaseous current through the mixture while subjected to said heat treatment whereby a large proportion of the initial cadmium content of the zincifcrous material is removed by volatilization without substantial loss of zinc.

9. The improvement in the treatment of zinciterous material containing cadmium which comprises mixing the material with a combustible agent and with an aqueous solution of a chloridizing agent until there is uniformly distributed throughout the material a sufli-cient amount of zinc chloride .to chloridize all thecadmium therein, and subjecting the resulting mixture to a sintering operation by blast-roasting in the course of which a large proportion of the initial cadmium content of the zinciferous material is removed by volatilization without substantial loss of zinc.

10. The improvement in the treatment of zinciferous material containing cadmium and/or lead which comprises subjecting the material to a heat treatment operation in the presence of a chloridizing agent and water vapor and under conditions of basicity :tavormium and/or lead without substantial loss of zinc.

11. The improvement in the treatment of zinciferous material containing cadmium and/or lead-which comprises subjecting the material to a heat treatment operation in thepresence of a chloridizing agent and Water vapor and under conditions incapable of forming strongly basic reaction products and thereby efliecting the removal from the-material by volatization of an. economically significant amount of cadmium and/or lead Without substantial loss of zinc.

12. The improvement in the treatment of zinciferous material containing cadmium and/0r lead which comprises subjecting the material to a sintering operation by blastroasting in the presence of a chloridizing agent and water vapor and under conditions of basicity favorable to efl'ective utilization of acidic compoundsof chlorine for chlori- (lizing cadmium and /or lead and thereby effecting the removal from the material by volatilization of an economically significant amount of cadmium and/ or lead without substantial loss of zinc.

13. The improvement in the treatment of zinciierous material containing cadmium and/or lead which comprises subjecting the material to a sintering operation by blastroasting in the presence of a chloridizing agent and water vapor and under conditions incapable of forming strongly basic reaction products and thereby effecting the removal from the material by volatilization of an economically significant amount of cadmium and/or lead without substantial loss of zinc.

14. The improvement in the treatment of zinciferous material containing cadmium and/or lead which comprises subjecting the material to a heat treatment operation in the presence of zinc chloride and water vapor and under conditions of basicity favorable to reflective utilization of acidic compounds of chlorine for chloridizing cadmium and /or lead and thereby effecting the removal from the material by volatilization of an economically significant amount of cadmium and/or lead without substantial loss of zinc.

15.- The improvement in the treatment of zinciferous material gontaining cadmium and/or lead which comprises subjecting the material to a heat treatment operation in the presence of zinc chloride and water vapor and under conditions incapable of forming strongly basic reaction products and thereby eifectingthe removal from the material by volatilization of an economically significant amount of cadmium and/or lead without substantial loss of zinc.

too

16. The improvement in the treatment of zinciferous material containing cadmium and/or lead which comprises subjecting the material to a sintering operation by blastroasting in the presence of zinc chloride and water vapor and under conditions of basicity favorable to effective utilization of acidic compounds of chlorine for chloridizing cadmium and/or lead and thereby effecting the removal from the material by volatilization of an economically significant amount of cadmium and/or lead without substantial loss of zinc. I

17. The improvement in the treatment of zinci'terous material containing cadmium and/or lead which comprises subjecting the material to a sintering operation by blastroasting in the presence of zinc chloride and water vapor and under conditions incapableoi forming strongly basic intermediary reaction products and thereby effecting the removal from the Zinciferous material by volatilization of a large proportion of its initial cadmium and or lead content without substantial loss of Zinc.

18. The improvement in the treatment of zinciferous' material containing cadmium and/or lead which comprises subjecting the material to a heat treatment operation in the presence of a chloridizing agent and water vapor and under conditions of basicity favorable to effective utilization of acidic compounds of chlorine for chloridizing cadmium and/or lead, andmaintaining a gaseous current'through the material while subjected to said heat treatment and thereby effecting the removal from the material by volatilization of an economically significant amount of cadmium and/or lead ,without substantial loss of zinc.

19; The improvement in the treatment of zinciferons material containing cadmium and/or lead which comprises subjecting the material to a heat treatment operation in the presence of zinc chloride and water vapor and under conditions incapable of forming strongly basic reaction products, and maintaining a gaseous current through the material while subjected to said heat treatment whereby a large proportion of the initial cadmium-and/or lead content of the zinciferous material is removed by volatilization without substantial loss of zinc.

20. The improvement in the treatment of zinciferous material containing cadmium and/or lead which comprises mixingthe material with an aqueous'solution of a chloridizing agent until there is uniformly distributed throughout the material a sufficient amount of zinc chloride to chloridize all the cadmium and/or lead therein, and subjecting the resulting mixture to a heat treatment operation in'the course of which a large proportion of the initial'cadmium and/or lead content of the zinciferous material is removed by volatilization without substantial loss of zinc.

.21. The improvement in the treat-ment of zinciferous material containing cadmium and/or lead wh ch comprises mixing the material with an aqueous solution of a chloridizing agent until there is uniformly distributed throughout the material a sufiicient amount of Zinc chloride to chloridize all the cadmium and /or lead therein, and subjecting the resulting mixture to a sintcring operation by blast-roasting in the course of which a large proportion of the initial cadmium and/or lead content of the zincifcrous material is removed by volatilization without substantial loss of zinc.

22. The improvement in the treatment of zinciferous material containing cadmium terial with an aqueous solution of hydrochloric acid containing sufiicient chlorine to chloridize all the cadmium and/or lead therein, and subjecting the resulting mixture to a heat treatment operation in the course of which a large proportion of the initial cadmium and/or lead content of the zinciferous material is removed by volatili- Zation without substantial loss of zinc.

23. The improvement in'the treatment of zinciferous material containing cadmium and/or lead which comprises mixing the material with an aqueous solution of hydro chloric acid containing sufficient chlorine to chloridize all the cadmium and/or lead therein, and subjecting the resulting mixture to a sintering operation by blast-roasting in the course of which a large-proportion of the initial cadmium and/or lead content of the zinciferous'materialis removed by volatilization without substantial loss of zinc.

QAQ The improvement in the treatment of zinciferous material containing cadmium and/or lead which comprises mixing the material with an acid and a chloride, and subjecting the resulting mixture to a heat treatment operation under conditions of basicity favorable to effective utilization of acidic compounds of chlorine for chloridizing cadmium and/or lead and thereby eiiecting the removal from the zinciferous material by volatilization of an economically significant amount of cadmium and/or lead without substantial loss of zinc.

25. The improvement in the treatment of zinciferous material containing cadmium and/or lead which comprises mixing the material with an aqueous solution of zinc chloride, and subjecting the resulting mixture to a heat treatment operation and there zinciferous material containing cadmium and/or lead which comprises mixing the 'material with an aqueous solution of zinc chloride,'subjecting the resulting mixture to a heat treatment operation, and maintaining a gaseous current through the material while subj ected to said heat treatment and thereby effecting the removal from the material by zinciferous material containing cadmium and/ or lead which comprises mixing the material with an aqueous solution of zinc chloride, subjecting the resulting mixture to a heat treatment operation and thereby effecting the removal from the material by volatilization of an economically significant amount of cadmium and/or lead without substantial loss of zinc, forming an aqueous solution of the volatilized chlorides and replacing cadmium and/or lead therein by zinc, and utilizing the resulting aqueous solution of zinc chloride for mixture with additional zinciferous material.

29. .The improvement in the treatment of @inciferous material containing cadmium and/or lead which comprises mixing the :ma-

' 6 terial with an aqueous solution of zinc chloride, subjecting the resulting mixture to a sintering operation by blast-roasting and thereby effecting the removal from the material by volatilization of an economically significant amount of cadmium and/or lead without substantial loss of zinc, forming an aqueous solution of the volatilized chlorides and replacing cadmium and/or lead therein by zinc, and utilizing the resulting aqueous solution of zinc chloride for mixture with additional zinciferous material. 7

' 30. The improvement in the treatment of zinciferous material containing cadmium and/or lead which comprises mixing the material with sulphuric acid and a chloride, and subjecting the resulting mixture to a heat treatment operation and thereby effecting the removal from the zinciferous material by volatilization of an economically significant amount of cadmium and/or lead without substantial loss of zinc.

31. The improvement in the treatment of zinciferous material containing cadmium and/or lead which comprises mixing the material with zinc sulfate and a chloride, and subjecting the resulting mixture to a heat treatment operation and thereby eflecting the removal from the zinciferous material by volatlllzation of an economically significant amountof-cadmium and/or lead without substantial loss of zinc. 7

32. The improvement in the treatment of zmciferous material containing cadmium and/or lead which comprises incorporating a substantial amount ofwater within the mass of the material with the minimum amount of work to form a fluff mixture, andsubjecting the resulting flufiy mixture to a sintering operation by blast-roasting in the presence of zinc chloride and-thereby effecting the removal from the material by volatilization of an economically significant amount of cadmium and/or lead without substantial loss of zinc. 5 -v 33. The improvement in the treatment of zinciferous material containing cadmium and/or lead. in; which the material is subjected to a sintering operation by blast-roasting in the presence of a chloridizing agent and water vapor characterized by subjecting the charge prepared for sintering to an ignition period prolonged several times beyond the time required to ignite the surface of the charge.

In testimony wheregf we aflix our signa tures.

HOWARD M. CYR. ROBERT K. WARING 

